Solid-state image pickup device and method of driving the same

ABSTRACT

An image sensor comprising a semiconductor substrate with a plurality of photoelectric conversion elements and a charge-voltage conversion element. The plurality of photoelectric conversion elements further includes at least a first photoelectric conversion element and a second photoelectric conversion element. The charge-voltage conversion element is shared by the first and second photoelectric conversion elements. The image sensor further includes a first charge accumulation element adjacent to the first photoelectric conversion element and at least a portion of the first charge accumulation element overlaps a charge accumulation region of the first photoelectric conversion element. The image sensor also includes a second charge accumulation element adjacent to the second photoelectric conversion element and at least a portion of the second charge accumulation element overlaps a charge accumulation region of the second photoelectric conversion element. Each of the plurality of photoelectric conversion is configured to receive light entered from a first surface of the semiconductor substrate. The first and second charge accumulation elements are formed on a second surface of the semiconductor substrate and the second surface is opposed to the first surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 14/079,103, filed Nov. 13, 2013, which claims thepriority from prior Japanese Priority Patent Application JP 2012-266002filed in the Japan Patent Office on Dec. 5, 2012, the entire content ofwhich is hereby incorporated by reference.

BACKGROUND ART

The present technology relates to a solid-state image pickup device andto a method of driving the same. In particular, the present technologyrelates to a solid-state image pickup device and a method of driving asolid-state image pickup device that are capable of improving imagequality.

There has been known a solid-state image pickup device that allowscapacitance in a floating diffusion (FD) region provided in a pixel tobe variable, and thereby adjusting efficiency of conversion, to avoltage, from an electric charge obtained by receiving light from asubject (for example, see Japanese Unexamined Patent ApplicationPublication (Translation of PCT Application) No. 2007-516654).

In such a solid-state image pickup device, when a signal amount issmall, that is, under a low-illuminance condition, sensitivity of thepixel is increased through reducing capacitance of the FD region, andthereby, conversion efficiency is increased. In contrast, when thesignal amount is large, that is, under a high-luminance condition, thesensitivity of the pixel is decreased through increasing the capacitanceof the FD region, and thereby, the conversion efficiency is decreased.Thus, dynamic range is increased.

In the solid-state image pickup device in which the capacitance of theFD region is variable, a capacitive element is provided between pixels,that is, on the same plane as that of the FD region and a photoelectricconversion element of the pixel, photoelectric conversion element andthe like. The capacitive element is connected to the FD region via aswitch for allowing the capacitance to be varied. Through turning on oroff the switch, switching between a state in which capacitance is addedto that of the FD region and a state in which capacitance is not addedto that of the FD region is performed. Thus, conversion efficiency isadjusted.

SUMMARY

In order to increase the dynamic range of a pixel, it is desirable toincrease a difference between high level and low level of conversionefficiency in the pixel. In order to increase the difference, it isnecessary to increase capacitance of the capacitive element that is tobe added to the capacitance of the FD region.

However, in the above-described technology, it is necessary to providethe capacitive element for adding capacitance to that of the FD regionbetween pixels that are adjacent to each other. Therefore, in order tosecure an area of the capacitive element, it is necessary to reduce thesize of elements such as a photodiode and a pixel transistor in thepixel.

Accordingly, for example, since an area of the photodiode is reduced, aphotoelectric conversion region of the solid-state image pickup devicebecomes small. Therefore, the light receiving sensitivity of the pixelis decreased. Accordingly, not only the S/N ratio (signal-to-noiseratio) but also the saturated signal amount of the photodiode isdecreased. As a result, the image quality of the image obtained by thesolid-state image pickup device is degraded. It is to be noted that, ingeneral, it is known that the area of the photodiode is proportional tothe saturated signal amount.

Moreover, in order to secure a large area of the capacitive element foradding capacitance to that of the FD region, it is necessary to reducethe size of the transistors arranged in the pixel as well. For example,when a size of an amplifier transistor that is used to read a voltage,that is, a signal level, obtained by receiving light from a subject isreduced, random noise is increased, which leads to a degradation inimage quality.

Moreover, for example, when the size of a transistor such as a selectiontransistor, a reset transistor, and a transfer transistor in the pixelis reduced, variations in transistor characteristics are increased.Therefore, noise is increased and S/N ratio is decreased. Accordingly,image quality is degraded.

It is desirable to provide a solid-state image pickup device and amethod of driving the same that are capable of improving image quality.

According to an embodiment of the present disclosure, there is providedan image sensor. The image sensor includes a semiconductor substratehaving a photoelectric conversion element and a charge-voltageconversion element. The sensor further includes a capacitance switch. Acharge accumulation element is located adjacent the photoelectricconversion element. At least a portion of the charge accumulationelement overlaps a charge accumulation region of the photoelectricconversion element. The charge accumulation element is selectivelyconnected to the charge-voltage conversion element by the capacitanceswitch.

In accordance with further embodiments, a capacitance of the chargeaccumulation element is added to a capacitance of the charge-voltageconversion element when the capacitance switch is closed. Alternativelyor in addition, the photoelectric conversion element can be providedbetween the charge accumulation element and a light receiving surface ofthe semiconductor substrate. The image sensor can further comprise aback illumination type image sensor in which the photoelectricconversion element is provided between a light receiving surface of thesemiconductor substrate and a wiring layer. Moreover, the chargeaccumulation element can be part of the wiring layer.

In accordance with further embodiments, the image sensor can include alight shielding layer. The charge accumulation element can be formed aspart of the light shielding layer. Moreover, the charge accumulationelement can be formed between the light shielding layer and thephotoelectric conversion element.

In accordance with still other embodiments, a plurality of photoelectricconversion elements and a plurality of charge-voltage conversionelements can share a single one of the charge accumulation elements. Thecharge accumulation element can include first and second electrodes,wherein a first one of the electrodes is connected to the capacitanceswitch. The charge-voltage conversion element can be a floatingdiffusion region, and the charge accumulation element can be acapacitor. In accordance with still other embodiments, the image sensorcan be a front illumination type image sensor, wherein thecharge-voltage conversion element is included in an image plane phasedifference pixel, and wherein the charge accumulation element operatesas a light shielding layer with respect to the charge-voltage conversionelement.

In accordance with further embodiments of the present disclosure, animaging apparatus is provided. The apparatus includes an optical sectionand a solid-state image pickup device operable to receive light from theoptical section. The solid-state image pickup device includes aphotoelectric conversion element, and a charge-voltage conversionelement. The solid-state image pickup device can further include acapacitance switch, and a charge accumulation element adjacent thephotoelectric conversion element. At least a portion of the chargeaccumulation element overlaps a charge accumulation region of thephotoelectric conversion element. The charge accumulation element can beselectively connected to the charge-voltage conversion element by thecapacitance switch. In addition, a digital signal processor can beincluded as part of the apparatus, wherein the digital signal processorreceives a signal from the solid-state image pickup device.

In accordance with still other embodiments, the photoelectric conversionelement of the apparatus is provided between the charge accumulationelement and a light receiving surface of a semiconductor substrate inwhich the photoelectric conversion elements are formed. The apparatuscan further include a wiring layer wherein the image sensor is a backillumination type image sensor in which the photoelectric conversionelement is provided between the light receiving surface of thesemiconductor substrate and the wiring layer. In addition, the chargeaccumulation element can be part of the wiring layer.

In accordance with still other embodiments, the apparatus can include alight shielding layer. Moreover, the charge accumulation element can beformed between the light shielding layer and the photoelectricconversion element.

In accordance with still other embodiments, a method of driving an imagesensor is provided. More particularly, a solid-state image sensorincluding a photoelectric conversion element, a charge-voltageconversion element, and a charge accumulation element are provided aspart of a solid-state image sensor. At least a portion of the chargeaccumulation element overlaps a charge accumulation region of thephotoelectric conversion element. The capacitance of the chargeaccumulation element is capable of being added to a capacitance of thecharge-voltage conversion element. According to the method, anilluminance condition is detected. In response to determining that theilluminance condition is low, the charge-voltage conversion element iselectrically disconnected from the charge accumulation element. Inresponse to determining that the illuminance condition is high, thecharge-voltage conversion element is electrically connected to thecharge accumulation element.

A capacitance switch can be provided to selectively connect the chargeaccumulation element to the charge-voltage conversion element. Moreparticularly, the capacitance switch is opened to electricallydisconnect the charge-voltage conversion element from the chargeaccumulation element. The capacitance switch is closed to electricallyconnect the charge-voltage conversion element to the charge accumulationelement.

According to further embodiments of the method, the solid-state imagesensor can be a back illumination type image sensor.

Alternatively, the solid-state image sensor can be a front illuminationtype sensor that includes an image plane phase difference pixel that canbe used for image plane phase difference autofocus, wherein the chargeaccumulation element operates as a light shielding layer of the imageplane phase difference pixel.

Additional features and advantages of embodiments of the presentdisclosure will become more readily apparent from the followingdescription, particularly when taken together with the accompanyingdrawings.

According to the above-described embodiments of the present technology,image quality is improved.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the technology as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate embodiments and,together with the specification, serve to explain the principles of thetechnology.

FIG. 1 is a diagram illustrating a configuration example of asolid-state image pickup device.

FIG. 2 is a diagram illustrating a configuration example of a pixel.

FIG. 3 is a diagram illustrating an arrangement example of a chargeaccumulation element.

FIG. 4 is a diagram illustrating a cross-section of the pixel.

FIG. 5 is a diagram for explaining switching of conversion efficiency.

FIG. 6 is a flow chart explaining an image pickup processing under alow-illuminance condition.

FIG. 7 is a flow chart explaining an image pickup processing under ahigh-illuminance condition.

FIG. 8 is a diagram illustrating a cross-section of a pixel.

FIG. 9 is a diagram illustrating an arrangement example of the chargeaccumulation element.

FIG. 10 is a diagram illustrating a cross-section of a pixel.

FIG. 11 is a diagram illustrating a cross-section of a pixel.

FIG. 12 is a diagram illustrating a cross-section of a pixel.

FIG. 13 is a diagram illustrating a cross-section of a pixel.

FIG. 14 is a diagram illustrating a cross-section of a pixel.

FIG. 15 is a diagram illustrating an arrangement example of the chargeaccumulation element.

FIG. 16 is a diagram illustrating a cross-section of a pixel.

FIG. 17 is a diagram illustrating a cross-section of a pixel.

FIG. 18 is a diagram illustrating a cross-section of a pixel.

FIG. 19 is a diagram illustrating a configuration example of an imagepickup apparatus.

DETAILED DESCRIPTION

Some embodiments of the present technology will be described below withreference to the drawings.

First Embodiment Configuration Example of Solid-State Image PickupDevice

First, description will be given of a configuration example of asolid-state image pickup device to which an embodiment of the presenttechnology is applied. FIG. 1 is a diagram illustrating theconfiguration example of the solid-state image pickup device to whichthe present embodiment of the present technology is applied.

A solid-state image pickup device 11 may be, for example, an imagesensor of a back illumination type that may be configured of, forexample, a CMOS (Complementary Metal Oxide Semiconductor) image sensoror the like. The solid-state image pickup device 11 receives light froma subject and performs photoelectric conversion on the received light togenerate an image signal, thereby picking up an image.

It is to be noted that an image sensor of a back illumination type has aconfiguration in which a photodiode is provided between a lightreceiving surface and a wiring layer. The light receiving surface is asurface on which the light from the subject is incident, and can includean on-chip lens that collects light. The wiring layer may includewirings, for example, of a transistor that drives each pixel, etc.

The solid-state image pickup device 11 includes a pixel array section21, a vertical drive section 22, a column processing section 23, ahorizontal drive section 24, a system control section 25, pixel drivelines 26, vertical signal lines 27, a signal processing section 28, anda data storage section 29.

In the solid-state image pickup device 11, the pixel array section 21 isformed on a semiconductor substrate (chip) which is not illustrated.Further, the vertical drive section 22, the column processing section23, the horizontal drive section 24, and the system control section 25are integrated on the semiconductor substrate.

The pixel array section 21 includes pixels that each include aphotoelectric conversion element that generates electric chargeaccording to an amount of light incident from a subject and accumulatesthe generated electric charge. The pixels included in the pixel arraysection 21 are arranged two-dimensionally in a horizontal direction (rowdirection) and in a vertical direction (column direction) in thedrawing.

For example, in the pixel array section 21, the pixel drive lines 26 arewired along the row direction for each pixel row that includes pixelsarranged in the row direction. Also, the vertical signal lines 27 arewired along the column direction for each pixel column that includespixels arranged in the column direction.

The vertical drive section 22 may be configured, for example, of a shiftregister, an address decoder, and/or the like. The vertical drivesection 22 supplies signals etc. to the respective pixels via theplurality of pixel drive lines 26, thereby driving all of the respectivepixels in the pixel array section 21 at the same time, or driving eachrow etc. of the respective pixels in the pixel array section 21.

The column processing section 23 reads signals from the respectivepixels via the vertical signal lines 27 for each pixel column in thepixel array section 21. The column processing section 23 performs, onthe read signals, processing such as denoising processing, correlateddouble sampling processing, and A-D (Analog-to-Digital) conversionprocessing, thereby generating pixel signals.

The horizontal drive section 24 may be configured, for example, of ashift register, an address decoder, and/or the like. The horizontaldrive section 24 sequentially selects unit circuits corresponding to thepixel columns in the column processing section 23. Through the selectivescanning by the horizontal drive section 24, the pixel signals, on whichthe signal processing is performed for each unit circuit in the columnprocessing section 23, are sequentially outputted to the signalprocessing section 28.

The system control section 25 may be configured, for example, of atiming generator that generates various timing signals, etc. The systemcontrol section 25 controls drive of the vertical drive section 22, thecolumn processing section 23, and the horizontal drive section 24, basedon the timing signals generated by the timing generator.

The signal processing section 28 performs, on the pixel signals suppliedfrom the column processing section 23, signal processing such asarithmetic processing and outputs the image signals configured of therespective pixel signals, while temporally storing data in the datastorage section 29 as necessary.

[Configuration Example of Pixel]

Next, description will be given of a configuration of each pixel in theabove-described pixel array section 21. FIG. 2 is a circuit diagramillustrating a configuration example of one pixel provided in the pixelarray section 21.

In FIG. 2, the pixel in the pixel array section 21 includes a photodiode61, a transfer gate element 62, a charge-voltage conversion element 63,a capacitance switch 64, a charge accumulation element 65, a reset gateelement 66, an amplifier transistor 67, and a selection transistor 68.

The photodiode 61 may be, for example, a photoelectric conversionelement that is configured of a PN-junction photodiode. The photodiode61 receives light from a subject, generates electric charge according toan amount of the received light through photoelectric conversion, andaccumulates the generated electric charge.

The transfer gate element 62 is provided between the photodiode 61 andthe charge-voltage conversion element 63. The transfer gate element 62transfers the electric charge accumulated in the photodiode 61 to thecharge-voltage conversion element 63 in response to a drive signal TRGthat is applied to a gate electrode of the transfer gate element 62.

For example, in FIG. 2, the transfer gate element 62, the capacitanceswitch 64, the reset gate element 66, and the selection transistor 68may be each comprise an N-channel MOS transistor.

Driving signals TRG, DCG, RST, and SEL are supplied to gate electrodesof the transfer gate element 62, the capacitance switch 64, the resetgate element 66, and the selection transistor 68, respectively. Thesedrive signals TRG, DCG, RST, and SEL are each a pulse signal that isactivated (ON) in a high level state and is inactivated (OFF) in a lowlevel state.

Accordingly, to give an example referring to the transfer gate element62, when the drive signal TRG supplied to the gate electrode of thetransfer gate element 62 is activated and the transfer gate element 62is allowed to be ON, the electric charge accumulated in the photodiode61 is transferred to the charge-voltage conversion element 63.

The charge-voltage conversion element 63 is a floating diffusion (FD)region that converts, into an electric signal, the electric charge thathas been transferred from the photodiode 61 via the transfer gateelement 62, and outputs the electric signal. The electric signal may be,for example, a voltage signal.

The charge-voltage conversion element 63 is connected to the reset gateelement 66, and is also connected to the vertical signal line 27 via theamplifier transistor 67 and the selection transistor 68. Further, thecharge-voltage conversion element 63 is connected, via the capacitanceswitch 64, to the charge accumulation element 65 that is a capacitorthat accumulates electric charge.

The capacitance switch 64 is turned on or off in response to the drivesignal DCG, thereby switching a connection state of the charge-voltageconversion element 63 and the charge accumulation element 65 between anelectrically-connected state and an electrically-disconnected state.

Specifically, the drive signal DCG is supplied to the gate electrodeconfiguring the capacitance switch 64. When the drive signal DCG is ON,potential just below the capacitance switch 64 becomes deep, whichallows the charge-voltage conversion element 63 to be electricallyconnected to the charge accumulation element 65.

On the other hand, when the drive signal DCG is OFF, the potential justbelow the capacitance switch 64 becomes shallow, which allows thecharge-voltage conversion element 63 to be electrically disconnectedfrom the charge accumulation element 65.

Accordingly, through allowing the drive signal DCG to be ON or OFF,capacitance is added to that of the charge-voltage conversion element 63and sensitivity of the pixel is varied. Specifically, a relationshiprepresented by ΔV=ΔQ/C is established where ΔQ is an amount of variationin the accumulated electric charge, ΔV is variation in a voltage at thattime, and C is a capacitance value.

The capacitance value C in a region in the pixel in which a signal levelis read is represented by C_(FD)+C_(CAP) in a state where the drivesignal DCG is ON, where a capacitance value of the charge-voltageconversion element 63 is C_(FD), and a capacitance value of the chargeaccumulation element 65 is C_(CAP). On the other hand, when the drivesignal DCG is OFF, the capacitance value C is varied to C_(FD), andtherefore, sensitivity of a voltage (an amount of variation in voltage)with respect to the amount of variation in electric charge is increased.

As described above, in the solid-state image pickup device 11, thesensitivity of the pixel is appropriately varied through allowing thedrive signal DCG to be ON or OFF. For example, when the drive signal DCGis allowed to be ON, the charge accumulation element 65 is electricallyconnected to the charge-voltage conversion element 63. Therefore, partof the electric charge that has been transferred from the photodiode 61to the charge-voltage conversion element 63 is accumulated not only inthe charge-voltage conversion element 63 but also in the chargeaccumulation element 65.

It is to be noted that, more in detail, the charge-voltage conversionelement 63 is also connected as necessary to the charge accumulationelement provided in the adjacent pixel in addition to the chargeaccumulation element 65. Further, the charge accumulation element 65 isadjacent to an opposite surface of the photodiode 61 from the lightreceiving surface thereof, that is, to a region on which the light fromthe subject is not incident. Also, the charge accumulation element 65 isso provided to overlap the photodiode 61. Therefore, the light from thesubject is prevented from being shielded by the charge accumulationelement 65. Accordingly, the amount of light incident on the photodiode61 is prevented from being decreased.

The reset gate element 66 is an element that initializes (resets) eachregion in the charge-voltage conversion element 63, the capacitanceswitch 64, and the charge accumulation element 65 as necessary. A drainof the reset gate element 66 is connected to a power source having apower source voltage VDD, and a source thereof is connected to thecharge-voltage conversion element 63. The gate electrode of the resetgate element 66 is supplied with the drive signal RST as a reset signal.

When the drive signal RST is activated, the reset gate element 66becomes conductive, and a potential at each of the charge-voltageconversion element 63 etc. is reset to a level of the power sourcevoltage VDD. In other words, the charge-voltage conversion element 63etc. are initialized.

A gate electrode of the amplifier transistor 67 is connected to thecharge-voltage conversion element 63, and a drain thereof is connectedto the power source having the power source voltage VDD. The amplifiertransistor 67 serves as an input section of a source follower circuitthat reads the electric charge obtained through the photoelectricconversion by the photodiode 61. In other words, since the source of theamplifier transistor 67 is connected to the vertical signal line 27 viathe selection transistor 68, the amplifier transistor 67 configures thesource follower circuit, together with a constant current sourceconnected to an end of the vertical signal line 27.

The selection transistor 68 is connected between the source of theamplifier transistor 67 and the vertical signal line 27. The gateelectrode of the selection transistor 68 is supplied with the drivesignal SEL as a selection signal. When the drive signal SEL isactivated, the selection transistor 68 becomes conductive, and the pixelprovided with the selection transistor 68 is selected. When the pixel isselected, the signal outputted from the amplifier transistor 67 is readby the column processing section 23 via the vertical signal line 27.

In each pixel, as the pixel drive lines 26 shown in FIG. 1, a pluralityof drive lines may be wired, for example, for each pixel row. Further,the vertical drive section 22 supplies the drive signals TRG, DCG, RST,and SEL to the pixel via the plurality of drive lines that serve as thepixel drive lines 26.

[Layout of Charge Accumulation Element]

Subsequently, description will be given of an arrangement example of thecharge accumulation element 65 provided in the pixel.

The charge accumulation element 65 may be, for example, so provided tooverlap the opposite surface of the photodiode 61 from the lightreceiving surface thereof, as shown in FIG. 3. It is to be noted that,in FIG. 3, the same numerals are used to designate correspondingcomponents in FIG. 2, and the description thereof will be appropriatelyomitted. Also, in the drawing, a square with a symbol “x” represents acontact connected to the gate electrode of the transistor etc.

In the example shown in FIG. 3, another pixel that includes a photodiode91, a transfer gate element 92, and a charge accumulation element 93 isso provided to be adjacent to the pixel that includes the photodiode 61.These two pixels share the charge-voltage conversion element 63, thecapacitance switch 64, the reset gate element 66, the amplifiertransistor 67, and the selection transistor 68. Further, the two pixelsshare the charge accumulation element 65 and the charge accumulationelement 93 that are provided in the respective pixels as well.

In this example, the surface shown in the drawing is on the wiring layerside that is opposite from the light receiving surface of the photodiode61, the photodiode 91, and the like.

The charge accumulation element 65 includes two electrodes, that is, anelectrode 94 and an electrode 95 that face each other. The electrodes 94and 95 each may be formed, for example, of metal such as aluminum,copper, gold, and silver.

The electrode 94 is so provided to be adjacent to a surface on thewiring layer side of the photodiode 61. The electrode 94 is connected toa wire 96 to which a voltage Vss is applied. For example, the voltageVss may be at a ground level (GND) or the like. It is to be noted that,when a connection part of the wire 96 provided on the substrate isisolated from other elements, for example, by being covered with aP-type semiconductor region, the voltage Vss to be applied to the wire96 may be, for example, the power source voltage VDD or the like.

Moreover, the electrode 95 that faces the electrode 94 is connected tothe capacitance switch 64 by the capacitor wire 97.

As with the charge accumulation element 65, the charge accumulationelement 93 includes electrodes 98 and 99 formed of metal. The electrode98 provided on the photodiode 91 is connected to a wire 100 to which thevoltage Vss is applied. The electrode 99 is connected to the capacitanceswitch 64 by a capacitor wire 101.

Accordingly, for example, when the drive signal DCG for the capacitanceswitch 64 is allowed to be ON, the charge-voltage conversion element 63is electrically connected to the charge accumulation elements 65 and 93.Therefore, for example, upon reading of a pixel value of the pixel thatincludes the photodiode 61, when the transfer gate element 62 is allowedto be ON while the transfer gate element 92 is OFF, the electric chargein the photodiode 61 is accumulated in the charge-voltage conversionelement 63, the charge accumulation element 65, and the chargeaccumulation element 93.

Accordingly, a voltage according to the electric charge accumulated inthe charge-voltage conversion element 63 and the like is applied to thegate electrode of the amplifier transistor 67 via an FD wire 102.According to the applied voltage, a voltage that is outputted to thevertical signal line 27 which is connected to a contact 103 via theamplifier transistor 67 and the selection transistor 68 is varied.Therefore, the variation in the voltage is read by the column processingsection 23 as the pixel signal.

On the other hand, for example, upon reading the pixel value of thepixel that includes the photodiode 91, the transfer gate element 62 isremained to be OFF, and the transfer gate element 92 is allowed to beON. Accordingly, the electric charge in the photodiode 91 is accumulatedin the charge-voltage conversion element 63, the charge accumulationelement 65, and the charge accumulation element 93. A voltage accordingto the accumulated electric charge is applied to the gate electrode ofthe amplifier transistor 67 via the FD wire 102. Further, a voltagevalue according to the voltage applied to the gate electrode of theamplifier transistor 67 is read by the column processing section 23 viathe selection transistor 68 and the vertical signal line 27.

Through allowing the electric charge to be accumulated not only in thecharge accumulation element 65 provided in the pixel but also in thecharge accumulation element 93 provided in the adjacent pixel asdescribed above, capacitance to be added to that of the charge-voltageconversion element 63 is increased. Accordingly, the dynamic range ofthe pixel value under the high-illuminance condition is furtherincreased.

The example in which the charge accumulation elements in the respectiveadjacent pixels are shared by the adjacent pixels is described above.However, it is to be noted that the charge accumulation element may notbe shared. In such a case, for example, only the charge accumulationelement 65 is electrically connected to the charge-voltage conversionelement 63 in the pixel that includes the photodiode 61 to addcapacitance to that of the charge-voltage conversion element 63.

When the arrangement shown in FIG. 3 is adopted, a cross-section of thepixel that includes the photodiode 61 may be, for example, as shown inan upper part of FIG. 4. It is to be noted that the same numerals areused to designate corresponding components in FIG. 3, and thedescription thereof will be appropriately omitted.

In the upper part of FIG. 4, the photodiode 61 is provided in a P-typesemiconductor region 131 provided on the substrate. A hatched region ofthe photodiode 61 indicates a charge accumulation region in which theelectric charge obtained through the photoelectric conversion by thephotodiode 61 is accumulated. Further, the electrode 94 of the chargeaccumulation element 65 is provided in a first metal layer 132 that isadjacent to the P-type semiconductor region 131. Further, the electrode95 of the charge accumulation element 65 is provided in a second metallayer 133 that is adjacent to the first metal layer 132.

The electrode 94 that configures the charge accumulation element 65 isconnected to the wire 96 to which the voltage Vss is applied. Theelectrode 95 is connected to the charge-voltage conversion element 63 bythe capacitor wire 97 via the capacitance switch 64.

Moreover, in FIG. 4, light from a subject is incident on the photodiode61 from a direction indicated by an arrow A11, that is, from theopposite side from the wiring layer that includes the first metal layer132 and the second metal layer 133. Therefore, the light from thesubject that travels toward the photodiode 61 is prevented from beingshielded by the charge accumulation element 65 provided on the wiringlayer side.

Moreover, in this example, the electrode 94 that is adjacent to thephotodiode 61 is formed of metal. Therefore, as shown by an arrow A12,part of light that passes through the vicinity of the photodiode 61 isreflected by the electrode 94 and is incident on the photodiode 61.Therefore, the electrode 94 allows a larger amount of light to be led tothe photodiode 61. In other words, efficiency of collecting the lightfrom the subject is improved.

In the solid-state image pickup device 11 of a back illumination type,the charge accumulation element 65 does not overlap a surface on whichlight is incident in the charge accumulation region of the photodiode61. Specifically, the charge accumulation element 65 is arranged so thatpart or all of the charge accumulation element 65 overlaps the chargeaccumulation region of the photodiode 61 when viewed from a sideopposite from a side, of the photodiode 61, on which the light from thesubject is incident. In other words, the charge accumulation element 65is not provided in the P-type semiconductor region 131 provided with thephotodiode 61 and the like, not in a region in which part of thetransistors such as the amplifier transistor 67 is arranged, but in aportion, of the photodiode 61, on which light is not incident.

An area of the charge accumulation element 65 and areas of the photodiodes 61, the amplifier transistor 67, and the like have been in arelation of trade-off. However, in the solid-state image pickup device11, a region in which the respective elements such as the photodiode 61are provided is sufficiently secured regardless of the area of thecharge accumulation element 65. In other words, it is not necessary toreduce size of the respective elements.

Accordingly, for example, the area of the photodiode 61 (the area of thephotoelectric conversion region) is allowed to be further increased.Therefore, light receiving sensitivity of the pixel and saturated signalamount are improved. As a result, the S/N ratio of the signal read fromthe pixel is improved while sufficiently securing the area of the chargeaccumulation element 65. Therefore, image having better image quality isobtained.

Similarly, the area of the amplifier transistor 67 is allowed to befurther increased regardless of the area of the charge accumulationelement 65. Therefore, increase in random noise is suppressed and imagequality is improved. Further, the area of the transfer gate element 62,the reset gate element 66, and the respective transistors such as theselection transistor 68 are allowed to be further increased. Therefore,variations in transistor characteristics are suppressed. Accordingly,degradation in S/N ratio is suppressed and an image having better imagequality is obtained.

Subsequently, description will be given of switching of conversionefficiency (capacitance) performed through controlling ON and OFF of thecapacitance switch 64. It is to be noted that, in a middle part and alower part of FIG. 4, a lateral direction indicates a spatial directionin the solid-state image pickup device 11, and a vertical directionindicates potential.

First, when a signal amount is small, that is, under the low-illuminancecondition, as shown in the middle part of the drawing, the capacitanceswitch 64 is allowed to be OFF, and the charge-voltage conversionelement 63 is remained electrically disconnected from the chargeaccumulation elements 65 and 93. Therefore, capacitance of thecharge-voltage conversion element 63 is allowed to be small. In otherwords, efficiency of conversion of the accumulated electric charge intovoltage is increased. In this case, the signal outputted from the pixelis increased.

In this example, the charge-voltage conversion element 63 iselectrically disconnected from the charge accumulation element 65 andfrom the charge accumulation element 93 (which is not illustrated in thedrawing). Therefore, the electric charge obtained by the photodiode 61is accumulated only in the charge-voltage conversion element 63. It isto be noted that the hatched region in the middle and lower parts ofFIG. 4 indicates a region in which electric charge is accumulated.

In contrast, when the signal amount is large, that is, under thehigh-illuminance condition, as shown in the lower part of the drawing,the capacitance switch 64 is turned on, and the charge-voltageconversion element 63 is electrically connected to the chargeaccumulation elements 65 and 93. Therefore, the capacitance of thecharge-voltage conversion element 63 is increased. In other words,efficiency of conversion of the accumulated electric charge into voltageis decreased.

In this example, when a high-level voltage is applied to the gateelectrode of the capacitance switch 64 and the capacitance switch 64 isturned on, the potential just below the gate electrode is lowered (isallowed to be deeper). Therefore, the potential of the charge-voltageconversion element 63 is combined with the potential of the chargeaccumulation elements 65 and 93. In other words, the charge-voltageconversion element 63 is electrically connected to the chargeaccumulation elements 65 and 93.

Accordingly, the electric charge obtained by the photodiode 61 isaccumulated in the charge-voltage conversion element 63, the chargeaccumulation element 65, and the charge accumulation element 93. In thiscase, capacitance of the charge accumulation elements 65 and 93 is addedto that of the charge-voltage conversion element 63. As a result, thecapacitance of the charge-voltage conversion element 63 is substantiallyincreased, and therefore, conversion efficiency is decreased. Therefore,the dynamic range of the pixel value of the pixel is increased.

When the capacitance of the charge-voltage conversion element 63 isvaried through turning on or off the capacitance switch 64 in such amanner, the conversion efficiency is varied as shown in a line graph C11in FIG. 5. It is to be noted that, in FIG. 5, the vertical axisindicates an output voltage, that is, a value of voltage read from thevertical signal line 27. The horizontal axis indicates intensity oflight that is incident on the photodiode 61.

For example, in a section T1 under a low-illuminance condition in whichlight intensity is weak, the capacitance switch 64 is OFF, andtherefore, the conversion efficiency is high. In other words, a slope ofthe line graph C11 is large. On the other hand, in a section T2 under ahigh-illuminance condition in which light intensity is strong, thecapacitance switch 64 is ON, and therefore, the conversion efficiency islow. In other words, the slope of the line graph C11 is small.

It is to be noted that switching between ON and OFF of the capacitanceswitch 64 may be performed in response to an instruction from a user, ormay be performed by the solid-state image pickup device 11 depending onintensity of light incident on the photodiode 61.

[Description of Image Pickup Processing]

Further, description will be given of image pickup processing that isperformed when an image of a subject is picked up by the solid-stateimage pickup device 11.

First, image pickup processing under the low-illuminance condition willbe described referring to a flow chart shown in FIG. 6. It is to benoted that this image pickup processing may be performed on therespective pixels at the same timing or at different timings. Further,at the beginning of the image pickup processing, the transfer gateelement 62, the transfer gate element 92, the capacitance switch 64, thereset gate element 66, and the selection transistor 68 are OFF.

In step S11, the vertical drive section 22 turns on the selectiontransistor 68 and allows a pixel to be selected.

In step S12, the vertical drive section 22 turns on the capacitanceswitch 64 and allows the charge-voltage conversion element 63 to beelectrically connected to the charge accumulation elements 65 and 93.

In step S13, the vertical drive section 22 turns on the reset gateelement 66 and allows the charge-voltage conversion element 63 and thecharge accumulation elements 65 and 93 to be initialized (reset). Inother words, the potentials at the charge-voltage conversion element 63and at the charge accumulation elements 65 and 93 are reset to a levelof the power source voltage VDD.

In step S14, the vertical drive section 22 turns off the capacitanceswitch 64 and the reset gate element 66. Thus, initialization of thecharge-voltage conversion element 63 and the charge accumulationelements 65 and 93 is completed.

In step S15, the column processing section 23 reads a voltage value, asa reset level, according to the potential at the charge-voltageconversion element 63 from the amplifier transistor 67 via the selectiontransistor 68 and the vertical signal line 27.

In step S16, the transfer gate element 62 transfers the electric chargeaccumulated in the photodiode 61 to the charge-voltage conversionelement 63 based on the control by the vertical drive section 22.

Specifically, light from a subject that is incident on the photodiodeduring an exposure period is converted into electric charge in thephotodiode 61. When the vertical drive section 22 turns on the transfergate element 62, the photodiode 61 is electrically connected to thecharge-voltage conversion element 63 by the transfer gate element 62,and the electric charge accumulated in the photodiode 61 is transferredto the charge-voltage conversion element 63. After the transfer of theelectric charge, the transfer gate element 62 is turned off asnecessary, and the charge-voltage conversion element 63 is electricallydisconnected from the photodiode 61.

It is to be noted that, under the low-illuminance condition, in order toincrease conversion efficiency, the charge-voltage conversion element 63continues to be electrically disconnected from the charge accumulationelements 65 and 93 after the initialization.

In step S17, the column processing section 23 reads a voltage value, asa signal level, according to the potential at the charge-voltageconversion element 63 from the amplifier transistor 67 via the selectiontransistor 68 and the vertical signal line 27. The column processingsection 23 determines a value of the pixel signal, that is, a pixelvalue of the pixel, based on the read reset level and the read signallevel, and outputs the determined pixel value to the signal processingsection 28. After the value of the pixel signal is determined, the imagepickup processing on the pixel to be processed is completed.

In the above-described manner, the solid-state image pickup device 11increases the conversion efficiency through electrically disconnectingthe charge-voltage conversion element 63 from the charge accumulationelements 65 and 93 under the low-illuminance condition, therebyincreasing sensitivity of the pixel.

Next, image pickup processing under the high-illuminance condition willbe described referring to a flow chart shown in FIG. 7. This imagepickup processing may be also performed on the respective pixels at thesame timing or different timings. Further, at the beginning of the imagepickup processing, the transfer gate element 62, the transfer gateelement 92, the capacitance switch 64, the reset gate element 66, andthe selection transistor 68 are OFF.

It is to be noted that processing in step S41 to step S45 are similar tothe processing in step S11 to step S15 in FIG. 6, and therefore, thedescription thereof will be omitted.

After the processing in step S45 is performed and the reset level isread, the vertical drive section 22 turns on the capacitance switch 64in step S46.

Accordingly, the charge-voltage conversion element 63 is electricallyconnected to the charge accumulation elements 65 and 93, and therefore,conversion efficiency is decreased.

After the charge-voltage conversion element 63 is electrically connectedto the charge accumulation elements 65 and 93 through the processing instep S46, it proceeds to step S47. The image pickup processing iscompleted after performing the processing in step S47 and step S48.However, the processing in step S47 and step S48 is similar to theprocessing in step S16 and step S17 in FIG. 6, and therefore,description thereof will be omitted.

It is to be noted that, in step S47, part of the electric chargetransferred from the photodiode 61 to the charge-voltage conversionelement 63 is accumulated also in the charge accumulation elements 65and 93.

In the above-described manner, the solid-state image pickup device 11decreases the conversion efficiency through electrically connecting thecharge-voltage conversion element 63 to the charge accumulation elements65 and 93 under the high-illuminance condition, thereby decreasingsensitivity of the pixel and increasing the dynamic range of the pixelvalue.

It is to be noted that, in the image pickup processing shown in FIG. 7,it is described that the capacitance switch 64 is turned on beforetransferring the electric charge in photodiode 61 after theinitialization of the charge-voltage conversion element 63 and the like.However, the capacitance switch 64 may be turned on after transferringthe electric charge in the photodiode 61. In this case, the signal levelis read after the capacitance switch 64 is turned on.

Moreover, after the initialization of the charge-voltage conversionelement 63 and the like, the capacitance switch 64 may be kept ONwithout being turned off. In this case, both the reading of the resetlevel and the reading of the signal level are performed in a state inwhich the charge-voltage conversion element 63 is electrically connectedto the charge accumulation elements 65 and 93.

Second Embodiment Configuration Example of Pixel

The example in which the electrode 94 and the electrode 95 configuringthe charge accumulation element 65 are provided in the first metal layer132 and in the second metal layer 133, respectively, is described above.However, it is to be noted that the electrode configuring the chargeaccumulation element 65 may be provided between the first metal layer132 and the photodiode 61.

In such a case, the pixels provided in the solid-state image pickupdevice 11 may be configured, for example, as shown in FIG. 8. It is tobe noted that, in FIG. 8, the same numerals are used to designatecorresponding components in FIG. 4, and the description thereof will beappropriately omitted.

In the example shown in FIG. 8, the charge accumulation element 65includes an electrode 161 and an electrode 162 that face each other. Theelectrodes 161 and 162 may each be configured, for example, of metalsuch as aluminum. However, since an interlayer between the electrodes161 and 162 is thin, a distance between the electrodes 161 and 162 isshort. Therefore, higher capacitance of the charge accumulation element65 is achieved.

Moreover, in this example, the electrode 161 is connected to theunillustrated wire 96 to which the voltage Vss is applied. The voltageVss may be, for example, at the ground level (GND) or the like. It is tobe noted that the electrode 161 may be connected to the power sourcehaving the power source voltage VDD. Further, the electrode 162 isconnected to the charge-voltage conversion element 63 via the capacitorwire 97 and the capacitance switch 64.

Third Embodiment Layout of Charge Accumulation Element

The example in which the two electrodes configuring the chargeaccumulation element 65 are formed of metal is described above. However,one of the two electrodes that is arranged on the photodiode 61 side maybe formed of polysilicon.

In such a case, the respective elements in the pixel may be arranged,for example, as shown in FIG. 9. It is to be noted that, in FIG. 9, thesame numerals are used to designate corresponding components in FIG. 3,and the description thereof will be appropriately omitted.

In the example shown in FIG. 9, the charge accumulation element 65 isprovided on an opposite surface of the photodiode 61 from the lightreceiving surface thereof. The charge accumulation element 65 includesan electrode 191 and the electrode 95 that face each other. For example,the electrode 191 adjacent to the photodiode 61, that is, the electrode191 arranged between the photodiode 61 and the electrode 95, may beformed of polysilicon. Further, the electrode 95 is formed of metal.

As with the charge accumulation element 65, the charge accumulationelement 93 also includes an electrode 192 and the electrode 99 that faceeach other. The electrode 192 provided on the photodiode 91 side isformed of polysilicon and the electrode 99 is formed of metal.

Moreover, as with the case shown in FIG. 3, the charge accumulationelements 65 and 93 are shared by two pixels and are provided to addcapacitance to that of the charge-voltage conversion element 63.

When the respective elements configuring the pixel have the arrangementshown in FIG. 9, a cross-section of the pixel that includes thephotodiode 61 may be, for example, as shown in FIG. 10. It is to benoted that, in FIG. 10, the same numerals are used to designatecorresponding components in FIG. 9, and the description thereof will beappropriately omitted.

In FIG. 10, the electrode 95 formed of metal is provided in the firstmetal layer 132, and the electrode 95 is connected to the charge-voltageconversion element 63 via the capacitor wire 97 and the capacitanceswitch 64.

The electrode 191 formed of polysilicon is provided between the firstmetal layer 132 and the photodiode 61, and is adjacent to the photodiode61. The electrode 191 is connected to the unillustrated wire 96 to whichthe voltage Vss is applied. For example, the voltage Vss may be, forexample, at the ground level or the like. However, the electrode 191 maybe connected to the power source having the power source voltage VDD.

Fourth Embodiment Configuration Example of Pixel

When the charge accumulation element 65 includes the electrode 191 andthe electrode 95 as shown in FIG. 10 and the photodiode 61 has aso-called HAD (Hole Accumulation Diode) structure, a negative bias maybe applied to the photodiode 61.

In such a case, the pixels provided in the solid-state image pickupdevice 11 may be configured, for example, as shown in FIG. 11. It is tobe noted that, in FIG. 11, the same numerals are used to designatecorresponding components in FIG. 10, and the description thereof will beappropriately omitted.

In the configuration shown in FIG. 11, a charge pump circuit 221 isfurther provided in addition to the configuration shown in FIG. 10. Theelectrode 191 adjacent to the photodiode 61 is connected not to the wire96 but to the charge pump circuit 221.

“HAD structure” refers to a structure in which an N-type semiconductorregion is formed in a P-type semiconductor region, in other words, astructure in which the N-type semiconductor region is sandwiched in theP-type semiconductor regions.

In general, in the photodiode having the HAD structure, it is consideredto increase concentration of boron included in the P-type semiconductorregion in order to suppress occurrence of dark current, white spot, etc.However, when the concentration of boron is increased, the N-typesemiconductor region becomes smaller, which leads to decrease insaturated signal amount. As a result, the dynamic range of the pixelvalue is decreased.

Therefore, in the pixel in the solid-state image pickup device 11 shownin FIG. 11, the charge pump circuit 221 applies a negative bias to theelectrode 191 formed of polysilicon, and thereby, a negative bias isapplied to the surface of the photodiode 61.

Through this application of the negative bias, concentration of hole inthe surface of the photodiode 61 is increased. Accordingly, a holeaccumulation layer is formed in part of the P-type semiconductor region131 on the surface of the photodiode 61. As a result, the hole in thehole accumulation layer is coupled to noise electron, and therefore,noise caused by the dark current, the white spot, etc. is reduced.Accordingly, an image having higher image quality is obtained. Further,in this case, it is not necessary to increase the concentration of boronin the P-type semiconductor region 131 that configures the photodiode61. Therefore, the N-type semiconductor region is prevented from beingsmaller and the saturated signal amount is prevented from beingdecreased.

Fifth Embodiment Configuration Example of Pixel

It is described above that one or both of the two electrodes configuringthe charge accumulation element 65 are formed of metal. However, both ofthe two electrodes may be formed of polysilicon.

In such a case, the pixels provided in the solid-state image pickupdevice 11 may be configured, for example, as shown in FIG. 12. It is tobe noted that, in FIG. 12, the same numerals are used to designatecorresponding components in FIG. 10, and the description thereof will beappropriately omitted.

In the example shown in FIG. 12, the charge accumulation element 65includes the electrode 191 and an electrode 251 that face each other.The electrodes 191 and 251 are provided between the photodiode 61 andthe first metal layer 132. Further, the electrodes 191 and 251 are eachformed of polysilicon.

The electrode 251 is connected to the charge-voltage conversion element63 via the capacitor wire 97 and the capacitance switch 64. Further, theelectrode 191 is connected to the unillustrated wire 96.

Sixth Embodiment Configuration Example of Pixel

Moreover, in the configuration shown in FIG. 12, a negative bias may beapplied to the electrode 191. In such a case, for example, the pixels inthe solid-state image pickup device 11 may be configured as shown inFIG. 13. It is to be noted that, in FIG. 13, the same numerals are usedto designate corresponding components in FIG. 11 and FIG. 12, and thedescription thereof will be appropriately omitted.

In the example shown in FIG. 13, the electrode 191 is connected not tothe wire 96 but to the charge pump circuit 221 in the configurationshown in FIG. 12. Therefore, the charge pump circuit 221 applies anegative bias to the electrode 191, and thereby, a negative bias isapplied to the surface of the photodiode 61. Accordingly, occurrence ofdark current, white spot, etc. is suppressed.

Seventh Embodiment Configuration Example of Pixel

Moreover, when the charge pump circuit 221 applies the negative bias tothe electrode 191, higher capacitance may be achieved through reducingthe thickness of the interlayer film in the charge accumulation element65.

In such a case, for example, the pixels in the solid-state image pickupdevice 11 may be configured as shown in FIG. 14. It is to be noted that,in FIG. 14, the same numerals are used to designate correspondingcomponents in FIG. 8 and FIG. 11, and the description thereof will beappropriately omitted.

In the example shown in FIG. 14, the charge accumulation element 65includes the electrode 191 and the electrode 162 that face each other.The electrode 191 is connected to the charge pump circuit 221 forapplying the negative bias. Further, the electrode 191 is formed ofpolysilicon, and the electrode 162 is formed of metal. Further, theelectrode 162 is connected to the charge-voltage conversion element 63via the capacitor wire 97 and the capacitance switch 64.

A distance between the electrodes 191 and 162 is short since theinterlayer film between the electrodes 191 and 162 is thin. Theelectrodes 191 and 162 are arranged between the photodiode 61 and thefirst metal layer 132. Accordingly, higher capacitance in the chargeaccumulation element 65 is achieved.

Eighth Embodiment Layout of Charge Accumulation Element

Moreover, in order to increase the capacitance of the chargeaccumulation element 65 per unit area, the electrodes in the chargeaccumulation element 65 may be provided in a planer direction or in avertical direction to form a pectinate shape, and thereby, aconfiguration that increases facing area may be achieved. In such acase, the respective elements in the pixel may be arranged, for example,as shown in FIG. 15. It is to be noted that, in FIG. 15, the samenumerals are used to designate corresponding components in FIG. 3, andthe description thereof will be appropriately omitted.

In this example, the charge accumulation element 65 includes electrodes281-1 to 281-4 and electrodes 282-1 to 282-5. The electrodes 281-1 to281-4 face the electrodes 282-1 to 282-5. Further, the electrodes 281-1to 281-4 are each connected to the charge-voltage conversion element 63via the capacitor wire 97 and the capacitance switch 64. The electrodes282-1 to 282-5 are each connected to the wire 96 to which the voltageVss is applied.

It is to be noted that, hereinafter, the respective electrodes 281-1 to281-4 may be simply referred to as “electrode 281” when it is notparticularly necessary to distinguish between the electrodes 281-1 to281-4. Further, hereinafter, the respective electrodes 282-1 to 282-5may be simply referred to as “electrode 282” when it is not particularlynecessary to distinguish between the electrodes 282-1 to 282-5.

In the charge accumulation element 65, the electrodes 281 and theelectrodes 282 are arranged alternately, and the electrode 281 and theelectrode 282 that face each other serve as one capacitor. By providingthe electrodes 281 and the electrodes 282 in a pectinate shape in such amanner, the capacitance of the charge accumulation element 65 isincreased.

Similarly, the charge accumulation element 93 includes electrodes 283-1to 283-4 and electrodes 284-1 to 284-5. The electrodes 283-1 to 283-4face the electrodes 284-1 to 284-5. Further, the electrodes 283-1 to283-4 are each connected to the charge-voltage conversion element 63 viathe capacitor wire 101 and the capacitance switch 64. The electrodes284-1 to 284-5 are each connected to the wire 100 to which the voltageVss is applied.

It is to be noted that, hereinafter, the respective electrodes 283-1 to283-4 may be simply referred to as “electrode 283” when it is notparticularly necessary to distinguish between the electrodes 283-1 to283-4. Further, hereinafter, the respective electrodes 284-1 to 284-5may be simply referred to as “electrode 284” when it is not particularlynecessary to distinguish between the electrodes 284-1 to 284-5.

In the charge accumulation element 93, the electrode 283 and theelectrode 284 that face each other serve as one capacitor. Further, thecharge accumulation element 65 and the charge accumulation element 93are each shared by two pixels, and are provided to add capacitance tothat of the charge-voltage conversion element 63.

When the respective elements configuring the pixel are arranged as shownin FIG. 15, a cross-section of the pixel that includes the photodiode 61may be, for example, as shown in FIG. 16. It is to be noted, in FIG. 16,that the same numerals are used to designate corresponding components inFIG. 15, and the description thereof will be appropriately omitted.

In an example shown in FIG. 16, the electrodes 281 and the electrodes282 that configure the charge accumulation element 65 are alternatelyarranged to face one another on a surface on the wiring layer side ofthe photodiode 61. In particular, the electrodes 281 are each providedin a part that extends from the surface of the photodiode 61 to thesecond metal layer 133. It is to be noted that, some of the electrodes281 and 282 are not illustrated in the drawing.

Ninth Embodiment Configuration Example of Pixel

The example in which the embodiment of the present technology is appliedto the solid-state image pickup device 11 of a back illumination type isdescribed above. However, the embodiment of the present technology maybe applied to an image sensor of a front illumination type. The imagesensor of a front illumination type refers to a image sensor that has aconfiguration in which the wiring layer is provided between the lightreceiving surface and the photodiode. The wiring layer includes wirings,for example, of a transistor driving each pixel and/or the like. Thelight receiving surface is a surface on which light from a subject isincident, and is, in other words, an on-chip lens. The photodiodereceives light from the subject.

For example, when the present embodiment of the present technology isapplied to the image sensor of a front illumination type, the presentembodiment of the present technology may be effectively applied to animage plane phase difference pixel as shown in FIG. 17. It is to benoted that, in FIG. 17, the same numerals are used to designatecorresponding components in FIG. 4, and the description thereof will beappropriately omitted.

The image plane phase difference pixel refers to a pixel that is usedfor image plane phase difference AF (Auto Focus), out of the pixelsconfiguring the solid-state image pickup device. The image plane phasedifference AF is a method to adjust focal point by utilizing a phasedifference, for example, between an image obtained through receivinglight in the image plane phase difference pixel in which right side ofthe light receiving surface is shielded from light and an image obtainedthrough receiving light in an image plane phase difference pixel inwhich left side of the light receiving surface is shielded from light.

In an example shown in FIG. 17, the wiring layer that includes the firstmetal layer 132, the second metal layer 133, and the like is provided onthe light receiving surface side of the photodiode 61, that is, in anupper part of the drawing. Further, a lens 311 and a color filter 312are provided on the upper side of the wiring layer in the drawing.

Accordingly, the light from the subject is collected by the lens 311 andis incident on the color filter 312. Part of the light that passesthrough the color filter 312 passes through the wiring layer and isincident on the photodiode 61.

In the configuration shown in FIG. 17, the charge accumulation element65 that includes the two electrodes 94 and 95 formed of metal isarranged between the photodiode 61 and the color filter 312. The chargeaccumulation element 65 serves as a light shielding layer of the imageplane phase difference pixel.

Specifically, the electrodes 94 and 95 are so arranged as to overlap apartial region on the left side, in the drawing, of the chargeaccumulation region of the photodiode 61. Therefore, part of the lightthat is collected by the lens 311 and passes through the color filter312 is shielded by the electrode 95 as shown by a dashed line in thedrawings and is prevented from being incident on the photodiode 61.

It is to be noted that the electrode 94 and the electrode 95 areprovided in the first metal layer 132 and in the second metal layer 133,respectively. The electrode 94 is connected to a wire to which thevoltage Vss is applied. The electrode 95 is connected to thecharge-voltage conversion element 63 via the capacitor wire 97 and thecapacitance switch 64.

In the above-described manner, the charge accumulation element 65 is soarranged as to overlap a region, in the charge accumulation region ofthe photodiode 61, on which the light from the subject is prevented frombeing incident, that is, a region to be shielded from light. Thus, thecharge accumulation element 65 is allowed to serve as the lightshielding layer of the image plane phase difference pixel. Accordingly,it is not necessary to reduce size of the respective elements,regardless of the area of the charge accumulation element 65.

Accordingly, the area of the photodiode 61 (the area of thephotoelectric conversion region) is allowed to be increased, which leadsto improvement in light receiving sensitivity of the pixel and saturatedsignal amount. As a result, S/N ratio of the pixel signal is improved,and thereby, an image having better image quality is obtained.

Moreover, the area of the amplifier transistor 67 is allowed to beincreased. Therefore, increase in random noise is suppressed, andthereby, image quality is improved. Further, the areas of the respectivetransistors such as the transfer gate element 62 are allowed to beincreased. Therefore, variations in the transistor characteristics aresuppressed. Accordingly, degradation in S/N ratio is suppressed, and animage having better image quality is obtained.

It is to be noted that, also in the configuration shown in FIG. 17, thecharge accumulation element provided in another pixel adjacent to thepixel that includes the photodiode 61 may be connected to thecapacitance switch 64, and that charge accumulation element may be used,together with the charge accumulation element 65, to add capacitance tothat of the charge-voltage conversion element 63. In other words, thecharge accumulation element in pixels that are adjacent to each othermay be shared by the adjacent pixels as with the case shown in FIG. 3.

Tenth Embodiment Configuration Example of Pixel

In FIG. 17, the example in which the charge accumulation element 65 isallowed to serve as a light shielding layer is described. However, thecharge accumulation element 65 may be arranged between the lightshielding layer and the photodiode 61. In such a case, the image planephase difference pixel that includes the photodiode 61 may beconfigured, for example, as shown in FIG. 18. It is to be noted that, inFIG. 18, the same numerals are used to designate correspondingcomponents in FIG. 17, and the description thereof will be appropriatelyomitted.

In FIG. 18, the charge accumulation element 65 includes an electrode 341and an electrode 342 that face each other. The electrodes 341 and 342are arranged between a light shielding layer 343 and the photodiode 61.

In this example, the charge accumulation element 65 does not serve asthe light shielding layer. Therefore, the electrodes 341 and 342 are notnecessarily formed of metal. Therefore, the electrodes 341 and 342 eachmay be formed, for example, of metal such as aluminum, copper, gold, andsilver, or may be formed, for example, of polysilicon or the like. Forexample, one of the electrodes 341 and 342 may be formed of metal andthe other thereof may be formed of polysilicon.

The light shielding layer 343 is configured of light shielding memberseach formed of metal. The light shielding members are provided in thefirst metal layer 132 and the second metal layer 133.

The electrode 341 in the charge accumulation element 65 is connected tothe charge-voltage conversion element 63 via the light shielding membersforming the light shield layer 343, the capacitor wire 97, and thecapacitance switch 64. Further, the electrode 342 in the chargeaccumulation element 65 is connected, via the light shielding membersforming the light shielding layer 343, to a wire to which the voltageVss is applied. It is to be noted that the light shielding memberconnected to the electrode 342 is electrically disconnected from thelight shielding member connected to the electrode 341.

Also when the charge accumulation element 65 is provided between thelight shielding layer 343 and the photodiode 61 as described above, itis not necessary to reduce the size of the respective elements,regardless of the area of the charge accumulation element 65. Therefore,an image having better image quality is obtained.

Configuration Example of Image Pickup Apparatus

It is to be noted that the embodiments of the present technology areapplicable to general electronic apparatuses that use the solid-stateimage pickup device in an image reading section (photoelectricconversion element). Examples of such electronic apparatuses mayinclude: image pickup apparatuses such as digital still cameras andvideo camcorders; portable terminal apparatuses that have an imagepickup function; and copy machines that use the solid-state image pickupdevice in the image reading section. The solid-state image pickup devicemay be formed as one chip, or may be in a module-like form having animage pickup function in which an image pickup section and a signalprocessing section are packaged together or in which an image pickupsection and an optical system are packaged together.

FIG. 19 is a diagram illustrating a configuration example of an imagepickup apparatus as an electronic apparatus to which the above-describedembodiments of the present technology is applied.

An image pickup apparatus 501 shown in FIG. 19 includes an opticalsection 511 including lens groups etc., a solid-state image pickupdevice (image pickup device) 512, and a DSP (Digital Signal Processor)circuit 513 that is a camera signal processing circuit. Further, theimage pickup apparatus 501 also includes a frame memory 514, a displaysection 515, a record section 516, an operation section 517, and a powersource section 518. The DSP circuit 513, the frame memory 514, thedisplay section 515, the record section 516, the operation section 517,and the power source section 518 are connected to one another via a busline 519.

The optical section 511 takes in incident light (image light) from asubject and forms an image on an image pickup plane of the solid-stateimage pickup device 512. The solid-state image pickup device 512converts, into an electric signal, an amount of incident light that isused to form the image on the image pickup plane in a pixel unit, andoutputs the electric signal as a pixel signal. The solid-state imagepickup device 512 corresponds to the above-described solid-state imagepickup device 11.

The display section 515 may be formed, for example, of a panel-typedisplay such as a liquid crystal panel and an organic EL (ElectroLuminescence) panel. The display section 515 displays moving image or astill image that has been picked up by the solid-state image pickupdevice 512. The record section 516 records the moving image or the stillimage that has been picked up by the solid-state image pickup device 512in a recording media such as a video tape and a DVD (Digital VersatileDisk).

The operation section 517 gives, based on operation by a user, operationinstructions related to various functions of the image pickup apparatus501. The power source section 518 appropriately supplies various powersources that serve as operation power sources of the DSP circuit 513,the frame memory 514, the display section 515, the record section 516,and the operation section 517 to these targets.

The above embodiments are described referring to the case as an examplein which the embodiments are applied to a CMOS image sensor in whichpixels that detect signal electric charge according to an amount ofvisible light as a physical amount are arranged in rows and columns.However, the present technology is not limited to CMOS image sensors butis applicable to other types of solid-image pickup devices.

The above-described embodiments of the present technology are notlimited to the image pickup device that detects distribution of anamount of incident visible light and picks up the distribution as animage. The above-described embodiments of the present technology areapplicable to a solid-state image pickup device that picks updistribution of incident amount of infrared ray, X-ray, particles, etc.as an image.

Moreover, the embodiments of the present technology are not limited tothe above-described embodiments and may be variously modified withoutdeparting from the scope of the gist of the present technology.

It is possible to achieve at least the following configurations from theabove-described example embodiments and the modifications of thedisclosure.

(1) A solid-state image pickup device including:

a photoelectric conversion element including a charge accumulationregion, the photoelectric conversion element performing photoelectricconversion on incident light and accumulating, in the chargeaccumulation region, electric charge obtained through the photoelectricconversion;

a charge-voltage conversion element accumulating the electric chargeobtained through the photoelectric conversion; and

a charge accumulation element adjacent to the photoelectric conversionelement, part or all of the charge accumulation element overlapping thecharge accumulation region, and the charge accumulation element addingcapacitance to capacitance of the charge-voltage conversion element.

(2) The solid-state image pickup device according to (1), wherein,

the charge accumulation element is provided in each pixel that includesthe photoelectric conversion element, and

the charge accumulation element provided in a predetermined pixel andthe charge accumulation element provided in another pixel adjacent tothe predetermined pixel add capacitance to the capacitance of thecharge-voltage conversion element, when the electric charge isaccumulated in the charge-voltage conversion element in thepredetermined pixel.

(3) The solid-state image pickup device according to (1) or (2), furtherincluding a switch performing switching between a state in which thecharge-voltage conversion element is electrically connected to thecharge accumulation element and a state in which the charge-voltageconversion element is electrically disconnected from the chargeaccumulation element.

(4) The solid-state image pickup device according to any one of (1) to(3), wherein

the solid-state image pickup device is of a back illumination type, and

the charge accumulation element is adjacent to an opposite surface ofthe photoelectric conversion element from a light incident surface ofthe photoelectric conversion element.

(5) The solid-state image pickup device according to (4), wherein

the charge accumulation element includes electrodes facing each other,and

one of the electrodes that is provided closer to the photoelectricconversion element is formed of metal.

(6) The solid-state image pickup device according to any one of (1) to(3), wherein

the solid-state image pickup device includes an image plane phasedifference pixel, and

the charge accumulation element is adjacent to a light incident surfaceof the photoelectric conversion element, and serves as a light shieldinglayer of the image plane phase difference pixel.

(7) The solid-state image pickup device according to any one of (1) to(3), wherein

the solid-state image pickup device includes an image plane phasedifference pixel, and

the charge accumulation element is provided between the photoelectricconversion element and a light shielding layer of the image plane phasedifference pixel, the light shielding layer shielding part of the lightincident on the photoelectric conversion element.

(8) The solid-state image pickup device according to any one of (1) to(7), wherein the charge accumulation element includes a first groupincluding a plurality of electrodes and a second group including aplurality of electrodes, the first group facing the second group, andeach of the first and second groups including the plurality ofelectrodes being arranged in a pectinate shape.

(9) The solid-state image pickup device according to any one of (1) to(8), further including a negative bias application section applying anegative bias to the photoelectric conversion element via the chargeaccumulation element.

(10) The solid-state image pickup device according to any one of (1) to(9), wherein the charge accumulation element includes electrodes facingeach other, one of the electrodes being formed of one of metal andpolysilicon, and the other of the electrodes being formed of one of themetal and the polysilicon.

(11) A method of driving a solid-state image pickup device with

a photoelectric conversion element including a charge accumulationregion, the photoelectric conversion element performing photoelectricconversion on incident light and accumulating, in the chargeaccumulation region, electric charge obtained through the photoelectricconversion,

a charge-voltage conversion element accumulating the electric chargeobtained through the photoelectric conversion, and

a charge accumulation element adjacent to the photoelectric conversionelement, part or all of the charge accumulation element overlapping thecharge accumulation region, and the charge accumulation element addingcapacitance to capacitance of the charge-voltage conversion element,

the method including:

allowing the photoelectric conversion element to convert the lightincident from a subject into the electric charge through thephotoelectric conversion; and

allowing the charge-voltage conversion element to accumulate theelectric charge obtained in the photoelectric conversion element.

[1] An image sensor, comprising:

a semiconductor substrate, including:

a photoelectric conversion element;

a charge-voltage conversion element;

a capacitance switch;

a charge accumulation element adjacent the photoelectric conversionelement, wherein at least a portion of the charge accumulation elementoverlaps a charge accumulation region of the photoelectric conversionelement, wherein the charge accumulation element is selectivelyconnected to the charge-voltage conversion element by the capacitanceswitch.

[2] The image sensor of [1], wherein a capacitance of the chargeaccumulation element is added to a capacitance of the charge-voltageconversion element when the capacitance switch is closed.

[3] The image sensor of [1] or [2], wherein the photoelectric conversionelement is provided between the charge accumulation element and a lightreceiving surface of the semiconductor substrate.

[4] The image sensor of any one of [1] to [3], further comprising:

a wiring layer, wherein the image sensor is a back illumination typeimage sensor in which the photoelectric conversion element is providedbetween a light receiving surface of the semiconductor substrate and thewiring layer.

[5] The image sensor of [4], wherein the charge accumulation element ispart of the wiring layer.

[6] The image sensor of any one of [1] to [5], further comprising: alight shielding layer.

[7] The image sensor of [6], wherein the charge accumulation element isformed as part of the light shielding layer.

[8] The image sensor of [6] or [7], wherein the charge accumulationelement is formed between the light shielding layer and thephotoelectric conversion element.

[9] The image sensor of any one of [1] to [8], wherein a plurality ofphotoelectric conversion elements and a plurality of charge-voltageconversion elements share a single one of the charge accumulationelements.

[10] The image sensor of any one of [1] to [9], wherein the chargeaccumulation element includes first and second electrodes, wherein afirst one of the electrodes is connected to the capacitance switch.

[11] The image sensor of any one of [1] to [10], wherein thecharge-voltage conversion element is a floating diffusion region, andwherein the charge accumulation element is a capacitor.

[12] The image sensor of any one of [1] to [11], wherein the imagesensor is a front illumination type image sensor, wherein thecharge-voltage conversion element is included in an image plane phasedifference pixel, and wherein the charge accumulation element operatesas a light shielding layer with respect to the charge-voltage conversionelement.

[13] An imaging apparatus, comprising:

an optical section;

a solid-state image pickup device operable to receive light from theoptical section, including:

a photoelectric conversion element;

a charge-voltage conversion element;

a capacitance switch;

a charge accumulation element adjacent the photoelectric conversionelement, wherein at least a portion of the charge accumulation elementoverlaps a charge accumulation region of the photoelectric conversionelement, and wherein the charge accumulation element can be selectivelyconnected to the charge-voltage conversion element by the capacitanceswitch; and

a digital signal processor, wherein the digital signal processorreceives a signal from the solid-state image pickup device.

[14] The apparatus of [13], wherein the photoelectric conversion elementis provided between the charge accumulation element and a lightreceiving surface of a semiconductor substrate in which thephotoelectric conversion elements are formed.

[15] The apparatus of [14], further comprising:

a wiring layer, wherein the image sensor is a back illumination typeimage sensor in which the photoelectric conversion element is providedbetween a light receiving surface of the semiconductor substrate and thewiring layer.

[16] The apparatus of [15], wherein the charge accumulation element ispart of the wiring layer.

[17] The apparatus of any one of [13] to [16], further comprising: alight shielding layer.

[18] The apparatus of [17], wherein the charge accumulation element isformed between the light shielding layer and the photoelectricconversion element.

[19] A method of driving an image sensor, comprising:

providing a solid-state image sensor, including:

a photoelectric conversion element;

a charge-voltage conversion element;

a charge accumulation element adjacent the photoelectric conversionelement, wherein at least a portion of the charge accumulation elementoverlaps a charge accumulation region of the photoelectric conversionelement, and wherein a capacitance of the charge accumulation element iscapable of being added to a capacitance of the charge-voltage conversionelement;

detecting an illuminance condition;

in response to determining that the illuminance condition is low,electrically disconnecting the charge-voltage conversion element fromthe charge accumulation element;

in response to determining that the illuminance condition is high,electrically connecting the charge-voltage conversion element to thecharge accumulation element.

[20] The method of [19], further comprising:

providing a capacitance switch, wherein the charge accumulation elementis selectively connected to the charge-voltage conversion element by thecapacitance switch.

[21] The method of [20], further comprising:

opening the capacitance switch to electrically disconnect thecharge-voltage conversion element from the charge accumulation element.

[22] The method of [20] or [21], further comprising:

closing the capacitance switch to electrically connect thecharge-voltage conversion element to the charge accumulation element.

[23] The method of any one of [19] to [22], wherein the solid-stateimage sensor is a back illumination type image sensor.

[24] The method of any one of [19] to [23], wherein the solid-stateimage sensor is a front illumination type sensor and includes an imageplane phase difference pixel, the method further comprising:

using the image plane phase difference pixel for image plane phasedifference auto focus, wherein the charge accumulation element operatesas a light shielding layer of the image plane phase difference pixel.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2012-266002 filedin the Japan Patent Office on Dec. 5, 2012 the entire content of whichis hereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations, and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. An image sensor, comprising: a semiconductor substrate, including: aplurality of photoelectric conversion elements, including at least afirst photoelectric conversion element and a second photoelectricconversion element; a charge-voltage conversion element, wherein thecharge-voltage conversion element is shared by the first and secondphotoelectric conversion elements; a first charge accumulation elementadjacent the first photoelectric conversion element, wherein at least aportion of the first charge accumulation element overlaps a chargeaccumulation region of the first photoelectric conversion element; and asecond charge accumulation element adjacent the second photoelectricconversion element, wherein at least a portion of the second chargeaccumulation element overlaps a charge accumulation region of the secondphotoelectric conversion element, wherein each of the plurality ofphotoelectric conversion elements is configured to receive light enteredfrom a first surface of the semiconductor substrate, and wherein thefirst and second charge accumulation elements are formed on a secondsurface of the semiconductor substrate, the second surface is opposed tothe first surface.
 2. The image sensor of claim 1, further comprising: awiring layer, wherein the image sensor is a back illumination type imagesensor in which the first and second photoelectric conversion elementsare provided between a light receiving surface of the semiconductorsubstrate and the wiring layer.
 3. The image sensor of claim 2, whereinthe first and second charge accumulation elements are part of the wiringlayer.
 4. The image sensor of claim 1, further comprising a lightshielding layer, wherein the first and second charge accumulationelements are formed as part of the light shielding layer.
 5. The imagesensor of claim 4, wherein the first charge accumulation element isformed between the light shielding layer and the first photoelectricconversion element, and wherein the second charge accumulation elementis formed between the light shielding layer and the second photoelectricconversion element.
 6. The image sensor of claim 1, wherein each of thefirst and second charge accumulation elements includes first and secondelectrodes, wherein a first one of the electrodes is connected to thecapacitance switch.
 7. The image sensor of claim 1, wherein thecharge-voltage conversion element is a floating diffusion region, andwherein each of the first and second charge accumulation elements is acapacitor.
 8. The image sensor of claim 1, wherein the image sensor is afront illumination type image sensor, wherein the first photoelectricconversion element is included in an image plane phase difference pixel,and wherein the first charge accumulation element operates as a lightshielding layer with respect to the first photoelectric conversionelement.